This invention relates to flexible high voltage gas-insulated cable for electric power distribution purposes, and more specifically relates to a novel construction for the central conductor of such cable to ensure improved flexibility and high current carrying capability.
High voltage gas-insulated cable is well known in the art wherein cable for carrying high voltages, typically 230,000 volts and above, is provided with a central conductor spaced within a concentric outer grounded housing by spaced insulator supports. A suitable electronegative gas, typically sulfur hexafluoride under positive pressure, fills the interior of the outer housing. Cables of this type are disclosed in U.S. Pat. No. 4,100,367, in the name of Netzel; U.S. Pat. No. 4,095,041, in the name of Netzel and Ponder; U.S. Pat. No. 4,101,730 in the name of Netzel; U.S. Pat. No. 4,122,298 in the name of Brandt.
The outer housing of the cable is conventionally corrugated with annular or spiral corrugations to improve the flexibility of the outer housing and to permit the cable, though of relatively large diameter, to be wound on reels capable of shipment on trucks or railroad cars.
The central conductor is also relatively flexible to permit the reeling of the cable and consists typically of a thin wall, corrugated copper core which receives elongated segmented stranded aluminum wire fillers contained on the outer diameter of the corrugated core by a thin walled, corrugated copper sheath. This structure is disclosed in U.S. Pat. No. 4,122,298 to Brandt and in U.S. Pat. No. 4,095,041 to Netzel and Ponder.
The structure of the central conductor using segmented stranded aluminum wire fillers is expensive and difficult to manufacture since specialized machinery is needed to make the segmented stranded filler. Moreover, it was found that the a-c to d-c resistance ratio as measured by thermal tests was about 1.6 to 1, which is relatively high.